In general, in linear DC motors such as voice coil motors, Fleming's rule applies, to wit: when a coil moves relative to a permanent magnet a force or thrust will be generated based upon the magnetic flux from the permanent magnet and the electric current flowing through the coil. The magnitude of the thrust is proportional to the magnitude of the magnetic flux and the magnitude of the current flow.
The charge that can flow through a conductive wire moving relative to a magnetic field is limited. To increase current flow, the conductive wire needs to be wound a multiple number of times to form a coil which will permit an induced current of increased magnitude to flow therethrough. The magnitude of a linear DC motor thrust is the sum of thrust vectors generated from each of the conductive wires in the coil.
A conductive cable for a coil of conventional technology uses either a round wire having a circular cross-section or a flat wire preferably of rectangular cross-section.
When using a round wire, as shown in FIG. 8, a round wire 1 is wound to form n rows and m layers, making n.times.m turns.
On the other hand, when using a flat wire having a flat rectangular cross-section, as shown in FIG. 9, a flat wire 2 is wound to form one row and m layers, making 1.times.m turns; or as shown in FIG. 10, a flat wire 2 is wound to form n rows and m layers, making n.times.m turns.
In general, the thrust generated from a coil wound with multiple turns of conductive wire will be equal to the sum of the thrust vectors generated from each of the turns of conductive wire if the magnitude of the magnetic force, the cross-sectional area of the conductive wire, and the number of turns are equal and assuming the vector directions generated in each of the conductive wires are made to be equal. In other words, the thrust for the entire coil can be maximized by aligning each of the conductive wires during winding.
Furthermore, under conditions such that the magnitude of the magnetic force, the cross-sectional area of a conductive wire, and the number of turns are equal, then the higher the proportion of the sum of the cross-section of conductive wires to the cross-section of the coil, the smaller the coil size. In other words, the size of the coil is inversely proportional to the conductive wire packing density for a wire of given size.
When winding a coil using a round wire 1 having a circular cross-section, as shown in FIG. 8, layers of round wire are formed with guiding spaces 3 between the round wires. The spaces 3 between the round wires of the first layer facilitate alignment of the round wire in the second layer.
However, when using a round wire 1 having a circular cross-section, it is difficult to wind the wire into a plurality of turns without causing an overlap from one row to the next after traversing one layer completely, i.e., it is not currently possible to traverse to the next layer without causing some misalignment when overlaying of the wire upon the next layer. The overlap causes a lateral displacement of wire between successive layers. The overlaid sections of wire will deviate from the other sections to limit the packing density of the wire in the coil. In addition, as shown in FIG. 8, the spaces 3 between adjacent round wires 1 also makes it difficult to wind the round wire 1 with high packing density. Moreover, the overlaid sections of wire need to be flattened to prevent the magnitude of the thrust from being affected.
On the other hand, when winding a coil having one row and m layers using a flat wire 2 of rectangular cross-section, as shown in FIG. 9, the space created between adjacent flat wires 2 can be smaller than that created between adjacent round wires 1. Accordingly, this configuration makes it possible to form one row of high density wound coil of flat wire.
Also, in this case, the flat wire 2 does not need to traverse left and right, therefore, the structure makes it possible to vertically align the layers of flat wire 2 in one row between successive turns.
However, when using a flat wire 2 to wind a coil having n rows and m layers, as shown in FIG. 10, it is again difficult to align the flat wire 2 during winding.
In other words, the ratio of the thickness to width of the flat wire 2 is limited and the number of turns the wire can make per row is also limited. To obtain a large thrust, the wire must be turned multiple times, as shown in FIG. 10, requiring multiple traversing of the flat wire 2 both to the left and to the right of each row.
When winding with round wire, the round wire 1 in the bottom layer, limits deviations of the round wire on upper layers in both the right and left directions, that is, the round wire 1 on upper layers can be aligned by aligning the first layer only. However, the use of flat wire 2, does not limit deviations of the flat wire 2 on adjacent layers in the right and left directions. The flat wire 2 should be aligned on all layers.
In general, the flat wire 2 may be made by flattening the round wire 1 into a wire of rectangular cross section. The dimensions of the flat wire 2 in the thickness direction can be relatively uniform, but dimensions in the width direction can hardly be uniform. This can make it difficult to align the flat wire 2 during winding.
In addition, as is the case for the round wire 1, the flat wire 2 must also traverse a layer completely before winding the next layer. If this requires overlaying the flat wire 2 upon making the next layer, a problem develops similar to the problem with round wire in that the overlaid sections cannot be accurately aligned.
The present invention permits winding a coil using a flat wire which can be accurately and readily aligned to form an electrical coil assembly of multiple coils and a multiplicity of turns.